poorly chicken looking really sick - very pale comb!!

My Fenning Coucou is nearly 1 years old. A couple of months ago she started having problems - think she may have sour crop as she was bobbing her head and her crop was very bloated and full of liquid. I researched this on the net and massaged her crop which made her sick. She seemed to get better but continued bobbing. She hasn't laid any eggs for quite a while. This last week she has really gone off colour! Her comb is quite shrivelled and a very weird pale colour. She isn't interacting with the rest of my chickens and just sits there. I have picked her up to examine her and she appears to have lost loads of weight but she fluffs her feathers up to cover this up! She doesn't eat or drink very much. I think its only a matter of time before she dies but I wondered if anyone had any advice? I love my chucks and I'm really sad that she is poorly. Is there anything I can do or should I just put her out of her misery???

Separate her from the others. Keep her warm and in a darker area. I put mine in a dog kennel in the house with a towel draped over most of it. Then you can moniter her food intake and bowel movements more accurately.

Check her vent for eggbound. Search this site and there is tons of info on the subject.